Hydraulic steering arrangement

ABSTRACT

The invention concerns a hydraulic steering arrangement ( 1 ) with an adjustable throttle, which has an internal rotary slide ( 2 ) with internal steering openings ( 4 ) in its circumferential wall and rotatable in relation to this, an external rotary slide ( 3 ) with external steering openings ( 7, 10 ) in its circumferential wall ( 8 ). The production of such steering arrangements must be inexpensive, yet a jamming during operation must be avoided. For this purpose, each of the external steering openings is made by a substantially radially extending bore ( 7 ), which penetrates part of the circumferential wall ( 8 ), and a following section ( 10 ) with reduced flow cross section.

The invention concerns a hydraulic steering arrangement with anadjustable throttle, which has an internal rotary slide with internalsteering openings in its circumferential wall and, rotatable in relationto this, an external rotary slide with external steering openings in itscircumferential wall.

Such a hydraulic steering arrangement is, for example, known from DE 3126 040 A1. Here the steering openings are shaped as grooves in thecircumferential walls of the individual rotary slides, which groovesextend from a front side of the rotary slide. In the neutral positionthese grooves are overlapping each other. In this connection,broadenings of the steering openings of the internal rotary slide areprovided, which broadenings are arranged on the outside of the internalrotary slide. This results in variable flow resistances, when the rotaryslides are turned in relation to each other. The more the two rotaryslides are turned in relation to each other, the more the flowresistance increases. Such steering arrangements are, for instance, usedin hydraulic steering units. If, as in the state of the art, thesteering openings are lying opposite each other in the neutral position,thus causing the lowest pressure drop, an “open centre” unit isconcerned.

On the one hand, the two rotary slides are rotatable in relation to eachother. On the other hand the unit comprising the two rotary slides isalso rotatable in a housing, for example to determine the pressure andthe direction of the hydraulic fluid in such a steering unit.

In this connection the problem occurs that the external rotary slidegets jammed in the housing, for example when the pressure inside therotary slide gets too high. Among things, this is caused by the factthat one axial end of the external rotary slide is weakened by thegrooves forming the steering openings. Between the grooves there are“legs”, which are only fixed at one end, so that they will spread whenacted upon by a pressure.

To remedy this problem, DE 33 02 001 A1 suggests that the end of therotary slide is provided with an additional ring, so that again bothends of the “legs” are fixed, and an expansion is only possible in themiddle of the “legs”. This procedure has in fact to a high degreedefused the problem. However, it requires an additional production step,namely the fixing of the ring, which makes the production moreexpensive.

It is the purpose of the invention to develop a steering arrangementfurther, so as to make the production more profitable, yet stillavoiding the jamming.

In a hydraulic steering arrangement of the kind mentioned in theintroduction this problem is solved according to the invention in thateach of the external steering openings is a substantially radiallyextending bore, which penetrates part of the circumferential wall, and afollowing section with reduced flow cross section.

This embodiment offers several advantages: The bores are relativelysimple to make during production. It is sufficient to place a boringtool on the radial outside and to make the bore. However, at least onepath will remain on the external steering slide in the area of its frontend next to the steering openings. This path is the area between thefront end and the beginning of the bore. This means that there is nosevering of the rotary slide in this area, meaning that here the rotaryslide cannot expand. Thus the fitting of an additional component is notrequired. As the bore is followed by a section with reduced flow crosssection, the bore can have a relatively large diameter, meaning that thediameter can be larger than the width of the grooves in the steeringarrangements known till now. Surprisingly, this has led to the resultthat the throttle characteristic of the steering arrangement has a lowerviscosity dependence than the steering arrangements known till now. Thereason for this is that the hydraulic fluid must only travel arelatively short way through a narrow area, which is less critical withregard to the viscosity dependence of the flow resistance. Additionally,this embodiment offers a lower pressure drop in the neutral position,which again leads to less noise. Thus, the result is not only asimplified production, but also an improved operational behaviour, thelatter caused by the constructive embodiment.

Preferably, the bore is a cylinder bore with constant cross section andconical top. Thus a quite normal drill can be used, and special toolsare not required. Through the selection of the bore diameter the flowresistance can be predetermined relatively accurately and repeatably.

Preferably, the section with reduced flow cross section is formed by agroove extending on the inside of the circumferential wall. Such agroove can be made with a relatively small width, as it does not have tobe very deep. Both sides of the groove are then joined by the remaininginside of the circumferential wall, which forms a sealing zone togetherwith the outside of the circumferential wall of the internal rotaryslide. The width of the groove can be smaller than in the state of theart. However, it can also remain exactly as wide, as it will then causea lower flow resistance in the neutral position. The throttle effectthen occurs, as also in the state of the art, through a partial coveringof the steering openings by the other rotary slide. This steeringcharacteristic is then to a large extent maintained, so that the newsteering arrangement can also be fitted in existing hydraulic plant orused as spare parts.

Preferably, the groove extends in the axial direction. This gives asymmetrical operation behaviour, meaning that the same throttle effectswill occur in both relative rotation directions of both rotary slides.

Preferably, the groove extends at least in one direction further thanthe diameter of the bore. Through a dimensioning of this groove, forinstance selecting height, width and length of the groove, the throttleeffect can be determined, which will be caused by a total or partialcovering of the groove by the internal rotary slide. As the dimensionsof the groove can easily be changed, this gives a high productionflexibility.

In a particularly preferred embodiment it is provided that the crosssection of the section with reduced flow cross section expands from thestart of the bore towards the inside of the circumferential wall. If agroove is used, it will expand. Now, the section with reduced flow crosssection can at the same time be used for changing the throttlecharacteristic on the relative turning of the two rotary slides. As theembodiment with a groove will anyway require a working of the inside ofthe circumferential wall of the external rotary slide to produce thegroove, it is not difficult at all also to provide an additionalwidening of the groove. The same applies in a similar way for otherembodiments of the section with reduced flow cross section.

In this connection it is advantageous that the steering openings of theinternal rotary slide penetrate the circumferential wall with a shapethat remains unchanged. A working of the outside of the circumferentialwall of the internal rotary slide is no longer required. The throttlecharacteristic resulting from the turning of both rotary slides inrelation to each other is then exclusively caused by the expansion ofthe section with reduced flow cross section, for instance the wideningof the groove. This simplifies the production.

Preferably, the section with reduced flow cross section is milled. Thisproduction method is particularly suitable for the forming of a groove.As the groove does not have to be very deep, the milling is rather easyto perform. As the cutter can be short in this case, the groove can bemade very accurately.

In an alternative embodiment the section with reduced flow cross sectionis shaped into the circumferential wall by spark erosion. This way ofproduction is always appropriate, when a complicated shape is concerned,for instance when the section with the reduced flow cross sectionexpands in the direction of the inside of the circumferential wall ofthe external rotary slide.

Advantageously, an additional similar bore is arranged next to the borein the axial direction. Thus the throttle resistance in the neutralposition is further decreased. The bore is similar to the one describedabove, that is, it is also followed by a section with reduced flow crosssection. Of course, the number of bores can also exceed two.

In the following the invention is described on the basis of preferredembodiments in connection with the drawings, showing:

FIG. 1 a first embodiment of a hydraulic steering arrangement in theneutral position

FIG. 2 a share of the steering arrangement in the throttle position

FIG. 3 an axial section in part view

FIG. 4 top view of the outside of an external rotary slide

FIG. 5 a steering arrangement of a second embodiment corresponding tothe presentation in FIG. 1

FIG. 6 the steering arrangement in FIG. 5 shown like in FIG. 2.

A steering arrangement 1 has an internal rotary slide and an externalrotary slide 3, which are rotatable in relation to each other from theneutral position shown in FIG. 1 into the maximum throttle positionshown in FIG. 2. Of course, also a rotation in the opposite direction ispossible.

The internal rotary slide 2 has steering openings, which are made asgrooves 4, which expand in the direction of the outside of thecircumferential wall of the rotary slide 2, where they form recesses 5.Next to the recesses 5 in the circumferential direction there is asealing area 6 on which the internal rotary slide 2 bears on theexternal rotary slide 3.

In this connection the grooves 4 of the internal rotary slide 2 extendfrom a front side of the rotary slide 2 in a manner not shown.

The external rotary slide 3 also has steering openings, which are in thepresent case formed by cylinder bores 7, which penetrate part of thecircumferential wall 8 of the rotary slide 3 with a constant diameter.At the inner end the bore 7 has a conical top 9.

In the area of this conical top 9, a groove 10 is made extending in theaxial direction into the inside of the circumferential wall 8 of theexternal rotary slide 3. This groove 10 is so deep that it opens intothe bore 7. The width of the groove 10 is smaller than the diameter ofthe bore 7. Therefore, it forms a section with a reduced flow crosssection.

In the axial direction, next to the bore 7, there is a similar bore 11.The groove 10 extends across this bore 11 and also opens into the bore11.

In the neutral position shown in FIG. 1 the groove 10 of the externalrotary slide 3 lies opposite to the groove 4 of the internal rotaryslide 2. Due to the relatively large diameter of the bore 7 and thecorrespondingly large diameter of the bore 11, there is only arelatively small pressure drop for the hydraulic fluid when passing theexternal rotary slide 3. The pressure drop on the internal rotary slide2 is comparable with that of a traditional steering arrangement. Intotal however, this results in a lower pressure drop and thus less noisein the neutral position. Additionally, this embodiment reduces theviscosity dependence of the throttling.

A rotation of the internal rotary slide 2 in relation to the externalrotary slide 3 (or vice versa) will cause a reduction of the depth ofthe recess 5 in the area lying opposite to the groove 10. An increasingrotation angle will thus also increase the throttle resistance. Withthis embodiment the throttle resistance is substantially determined bythe depth of the recess 5 in each individual position. In the zone nextto the neutral position the recess 5 still has a relatively large depth,so that it is not of very large importance if both rotary slides 2, 3are not exactly in the neutral position. The throttle still haspractically the same resistance than in the exact neutral position.

The production of the steering arrangement is relatively simple. Whilethe internal rotary slide 2 can be produced as usual, that is, underformation of grooves extending from one front end, the formation ofsteering openings in the external rotary slide merely requires bores 7,11 from the radial outside into the circumferential wall 8 of theexternal rotary slide 3. Further, it is necessary to produce the grooves10. Both bores and grooves can be made with traditional tools, give nosevere problems and offer sufficient accuracy. However, the externalrotary slide does not loose firmness in this process, meaning that ajamming in a housing (not shown), in which the external rotary slide isrotatably encased, is more unlikely.

The groove 10 cannot only be made by milling, it can also be made in aspark erosion process.

Such a production process is particularly suited for the embodimentshown in FIGS. 5 and 6. Corresponding parts are provided with dashedreference numbers.

The internal rotary slide 2′ no longer has recesses on itscircumference. On the contrary it is made with cylinder shape, whendisregarding the grooves 4.

The recesses 5′ have now been moved to the external rotary slide 3′.They are made in that the groove 10′ extends in the direction of theinside of the circumferential wall 8′ of the external rotary slide 3′.Thus the function will remain the same, namely the more or lesscomprehensive covering of the opening of the groove 4 through the moreor less deep recess 5′, the depth of this recess depending on therotation angle.

Otherwise, the embodiment according to the FIGS. 5 and 6 correspond tothat of the FIGS. 1 to 4, that is, the steering openings in the externalrotary slide 3′ are made as bores 7′ extending into the groove 10′.

Also here the production of the bores 7′ are made with ordinary drillswith conically extending top, and the formation of the groove 10′ withthe following expansion, which later forms the recess 5′, takes placethrough spark erosion. Thus, the sealing area 6′ will occur between therecesses 5′ on the inside of the external slide 3′.

What is claimed is:
 1. Hydraulic steering arrangement with an adjustablethrottle, having an internal rotary slide with internal steeringopenings in its circumferential wall and, rotatable in relation to theinternal rotary slide, an external rotary slide with external steeringopenings in its circumferential wall, each of the external steeringopenings comprising a substantially radially extending bore whichpenetrates part of the circumferential wall of the external rotary slideand a following section with reduced flow cross section.
 2. Steeringarrangement according to claim 1, in which the bore is a cylinder borewith constant cross section and conical top.
 3. Steering arrangementaccording to claim 1, in which the section with reduced flow crosssection is formed by a groove extending on the inside of thecircumferential wall.
 4. Steering arrangement according to claim 3, inwhich the groove extends in an axial direction.
 5. Steering arrangementaccording to claim 3, in which the groove extends at least in onedirection further than the diameter of the bore.
 6. Steering arrangementaccording to claim 1, in which the cross section of the section withreduced flow cross section expands from the start of the bore towardsthe inside of the circumferential wall of the external rotary slide. 7.Steering arrangement according to claim 6, in which the steeringopenings of the internal rotary slide penetrate the circumferential wallof the internal rotary slide with a shape that remains unchanged. 8.Steering arrangement according to claim 1, in which the section with thereduced flow cross section is milled.
 9. Steering arrangement accordingto claim 1, in which the section with reduced flow cross section isshaped into the circumferential wall by spark erosion.
 10. Steeringarrangement according to claim 1, in which an additional similar bore isarranged in the external rotary slide next to the bore in an axialdirection.